1. Field of the Invention
Embodiments of the invention generally relate to an apparatus and method for reducing reflection characteristics in optical components. More particularly, embodiments of the invention relate to using a glass spacer in an optical component to minimize reflectance back into an optical fiber or source.
2. Description of the Related Art
One challenge associated with optical signal transmission technology, and in particular, with interconnecting various optical signal transmission components, is that the interconnection between components inherently results in a percentage of the optical signal transmitted therethrough being reflected either back in the direction from which it was originally transmitted or in another direction that does not correspond to the desired transmission direction. Regardless of the reflection direction, the percentage of the optical signal that is reflected is no longer transmitted, and therefore, at a minimum the signal strength is reduced, or more importantly, portions of the data stream may be lost. Therefore, it is desirable to design optical interconnections having a minimal amount of reflectance, wherein reflectance is generally defined as the ratio of the reflected power to incident power, which is generally expressed in dB or a percentage of the total optical signal power. Further, since reflection loss is generally defined as a discontinuity or impedance mismatch between the ratio of the incident power to the reflected power, reflection loss (Lr) may be represented by the following equation,
            L      r        =                  20        ⁢                                  ⁢                  log          10                ⁢                                                                      Z                1                            -                              Z                2                                                                    Z                1                            +                              Z                2                                                                  =              10        ⁢                                  ⁢                  log          10                ⁢                                            (                                                Z                  1                                -                                  Z                  2                                            )                        2                                              (                                                Z                  1                                +                                  Z                  2                                            )                        2                                ,wherein Z 1 and Z 2 are the respective impedances of the two optical devices or components being connected together, and the vertical bars designate absolute magnitude. Furthermore, it is generally known that in an optical fiber, a loss takes place at any discontinuity in the refractive index between the optical signal transmission mediums, especially at an air-glass interface, such as a fiber endface, at which a fraction of the optical signal is reflected back toward the source. It is to be noted that this reflection loss is also called a Fresnel reflection loss or simply Fresnel loss. In accordance with the Fresnel principles, at normal incidence, the fraction of reflected power may be expressed by the formula,
            L      f        =          10      ⁢                          ⁢              log        10            ⁢                                    (                                          n                1                            -                              n                2                                      )                    2                                      (                                          n                1                            +                              n                2                                      )                    2                      ,where n 1 and n 2 are the respective indices of refraction.
Inasmuch as the reflectance is known to interfere with efficient signal transmission, it is desirable to minimize and/or eliminate reflectance characteristics.